Several sending/reception systems, comprising multiple antennas are already known. Some of the systems use space-time encoding by which their spatial/temporal diversity can be exploited with the utmost efficiency. However, the spectral efficiency of these space-time codes is limited.
Certain research work then led to the study of layered space-time (LST) systems using spatial multiplexing techniques to obtain systems whose capacity increases linearly with the number of transmit and receiver antennas.
Thus Foschini, in “Layered Space-Time Architecture for Wireless Communication in a Fading Environment When Using Multiple Antennas” (Bell Laboratories Technical Journal, Vol. 1, No. 2, Autumn, 1996, pp. 41-59) presented a first space multiplexing system aimed at augmenting the capacity of transmission systems. To this end, he described a diagonal “BLAST” structure (known as D-BLAST) in which the coded or non-coded and interleaved symbols of each layer are transmitted successively by each of the transmit antennas.
Wolniansky, Foschini, Golden and Valenzuela, in “V-BLAST: An Architecture for Realizing Very High Data Rates Over the Rich-Scattering Wireless Channel” (Proc. ISSSE-98, Pisa, Italy, Sep. 29, 1998), subsequently simplified this technique by modifying the architecture of the initial “BLAST” system into a vertical system (“V-BLAST”) without encoding, and by using an interference cancellation algorithm at reception with a zero forcing (ZF) criterion. This vertical architecture quite simply proceeds from a demultiplexing of the chain of information into sub-chains, each of them being transmitted by its respective antenna.
Subsequently, Baro, Bauch, Pavlic and Semmler (“Improving BLAST Performance using Space-Time Block Codes and Turbo Decoding”, Globecom 2000, November 2000) envisaged the combination of the space-time codes and turbo-decoding with codes V-BLAST type systems.
Finally, Ma and Giannakis (“Full-Diversity Full-Rate Complex-Field Space-Time Coding”, IEEE Transactions on Signal Processing 2003) presented a technique combining linear precoding with MIMO techniques of spatial multiplexing at the time of sending. In this technique, linear precoding is done by the use of particular precoding matrices based on Vandermonde matrices, the different symbols at the time of sending being sent cyclically. The decoding in reception is done according to a maximum likelihood detector.
A first drawback of the “BLAST” technique of spatial multiplexing proposed by Foschini is its decoding complexity.
Another drawback of this technique, which was subsequently changed into the “V-BLAST” technique, is that the maximum spatial diversity of the systems is not exploited.
As for the technique envisaged by Baro, Bauch, Pavlic and Semmler, which consists in combining the space-time codes with the V-BLAST system, it has the drawback of not exploiting the maximum capacity of the system.
Furthermore, the different prior art techniques cannot be used to process correlated channels.
These different drawbacks are partially resolved by the technique of Ma and Giannakis, which can be used to exploit both the space-time diversity of the systems, by means of linear precoding, and their maximum capacity.
However, a major drawback of this technique is the receiver used, which must be of the maximum likelihood (abbreviated as ML) type. These ML receivers are complex to implement and, owing to their complexity, limit the size of the precoding matrix to the number of transmit antennas of the system.